We are trying to understand the regulation of the dopa carboxylase (DDC) gene of Drosophila melanogaster. We have isolated the chromosomal DDC gene from a library of chromosomal DNA sequences cloned in bacteriophage lambda. The DDC DNA is being used as a specific probe to detect RNA trascripts made from the DDC gene in vivo, and also to study the DNA sequences within and around the coding sequences. These studies should allow us to determine whether the primary mode of DDC gene regulation is transcriptional or post-transcriptional. We are also studying DNA sequences adjacent to the DDC gene, attempting to correlate transcripts with known lethal complementation groups.